Molded surface fastener, and method and apparatus for manufacturing the same

ABSTRACT

A molded surface fastener comprises: a substrate sheet; and a multiplicity of engaging elements standing on one surface of the substrate sheet, each of the engaging elements being composed of a stem rising from the one surface of the substrate sheet, and an engaging head projecting from an upper end of the stem for detachably engaging a companion loop. After a surface fastener is manufactured on a die wheel by continuous injection molding as a primary-intermediate, a heating and pressing roller disposed downstream of the die wheel presses the engaging head, while heating, to bend the engaging head from the stem and, at the same time, to form a pair of protuberances projecting in opposite directions from opposite side edges of the top of the engaging head perpendicularly with respect to a direction lengthwise of the engaging head.

This is a division, of application Ser. No. 08/742,202, filed Oct. 31,1996.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a synthetic resin molded surface fastenercomposed of a substrate sheet with a multiplicity of engaging elementson the substrate sheet and manufactured by extrusion, continuousinjection, or injection molding, and a method and an apparatus formanufacturing the molded surface fastener. More particularly, theinvention relates to a molded surface fastener which has minute-sizeengaging elements for reliable engagement with minute-size loops, whichprovides secure adequate engaging strength, adequate peeling resistanceand a high rate of engagement, which has good durability for repeateduse, and is suitable for use in paper diaper or similar goods.

2. Description of the Related Art

Integrally molded surface fasteners in which a substrate sheet and amultiplicity of hooks are integrally and continuously molded usingthermoplastic resin are disclosed in, for example, U.S. Pat. Nos.4,984,339 and 5,441,687. In recent years, application of this kind ofsurface fasteners is on the increase as connectors for industrialmaterials, vehicle or interior ornaments and daily goods as well asvarious kinds of sanitary goods, such as paper diapers. Consequently,various sizes and shapes of engaging elements formed on a surface of thesubstrate sheet are required to cope with the above-mentioned varioususes.

However, as is understood from the above-mentioned U.S. PatentSpecifications, it is a common knowledge that with the conventionalmolding apparatus for continuous, integrally molded surface fastener, itis difficult to obtain an acceptable molded surface fastener that isdelicate, and excellent in touch, in view of technological difficulty inthe molding process. Assuming that minute-size engaging elements weremolded, only a very low degree of strength could be achieved, so thatthe resulting molded surface fastener was of little practical use.Further, in the foregoing integrally molded hook-shape structure, thestem has a simple cross-sectional shape and can bend transversely orlongitudinally of the engaging element row from its base end much easierwhen the size of the engaging elements is smaller. In addition, for thesimple shape and excessive softness of the hook-shape engaging elements,adequate engaging strength could not be secured so that the engagingelements can be easily removed off the companion loops. As a result, theengaging elements gradually became unable to restore their originalposture after repeated use, thus reducing the rate of engagement withthe loops in a short period of time. Further, hook-shape engaging headsmolded as mentioned above had a low degree of engaging strength becauseof their simple shapes and excessive softness, so that they were easilyout of engagement. Therefore, in order to obtain adequate rigidness andadequate engaging strength, it was considered necessary to increase theindividual hook-shape engaging elements in size, making the resultingengaging elements too rigid and reducing the number of hooks per unitarea (hook density). As a result, the molded surface fastener becameunable to engage minute-size companion loops.

In order to overcome the foregoing problems, integrally molded surfacefasteners having minute-size engaging elements were proposed by, forexample, International Publication No. WO94/23610, U.S. Pat. No.5,077,870, Japanese Patent Laid-Open Publications Nos. Hei 2-5947 (U.S.Pat. No. 4,894,060).

The engaging elements of the molded surface fastener disclosed inInternational Publication No. WO94/23610 and U.S. Pat. No. 5,077,870have mushroom shapes instead of hook shapes. As compared to the priorart hook-shape engaging elements, the mushroom-shaped engaging elementscan secure a desired degree of strength in engagement with the companionloops though they are reduced to a minute size. Therefore, themushroom-type surface fastener is suitable for uses requiring adequatesoftness. However, with the engaging element having such a structure,the neck portion connecting the stem and its engaging head getsentangled with a plurality of loops at the time of engagement with thecompanion loops, tends to be broken at the neck portion and is thereforenot durable for repeated use.

The molded surface fastener disclosed in Japanese Laid-Open PublicationNo. Hei 2-5947 has an ordinary hook-type structure well known in theart, in which a multiplicity of generally J-shape or palm-tree-shapeengaging elements stand on the substrate sheet. However, this moldedsurface fastener can be manufactured inexpensively and can be used witha non-woven-cloth companion surface fastener, which also can bemanufactured inexpensively as compared to an ordinary fiber pile wovencloth. Therefore, this molded surface fastener is particularly suitablefor use in various disposable underwear and paper diaper. In the moldedsurface fastener, considering that adequate peeling resistance withrespect to pile fibers of a non-woven cloth cannot be obtained by theminute-size single-head engaging element, the density of engagingelements is set to be relatively large in an effort to provide generalengaging and peeling strength with respect to the minute pile fibers.

As with the engaging element disclosed in the abovementionedpublication, merely making the engaging element very small in size andlarge in density or only changing the shape of the engaging elementsinto a simple one, does not assure the required shearing strength andthe peeling strength during engagement with the companion non-wovencloth. So, even if the density of the hook-shape engaging elements isextremely large, the engaging heads push down the very soft fiber loops,which are closely and randomly arranged, of the companion non-wovencloth or fall flat themselves when an attempt is made to penetrate thehook-shape engaging heads into the dense fiber loops. As a result, theengaging elements become unable to penetrate into the fiber loops, so alowered rate of engagement as compared to the ordinary surface fastenercannot be avoided.

For the foregoing reasons, in the molded surface fastener having theabove-mentioned minute-size engaging elements, limitation wouldnecessarily occur either in reducing the size of the engaging elementsor in increasing the density of the engaging elements. The disclosure ofJapanese Patent Laid-Open Publication No. Hei 2-5947 is totally silentabout critical values, though the preferable parameters of variousportions of the engaging element are defined, in which the density ofengaging elements is preferably 70-100/cm², the height of engagingelements is 0.8-1.1 mm, the thickness of stem and the width of engaginghead (horizontal width perpendicular to an extending direction thelength of the engaging head) is preferably 0.46 mm, the width of thestem (thickness in the extending direction lengthwise of the engaginghead) is 0.18-0.30 mm, and the length of engaging head projecting fromthe stem is preferably 0.25-0.37 mm or less than 1 mm.

These numeric values are determined to provide the integrated strengthin both the shearing direction and the peeling direction, since theengaging element has an ordinary shape considering no unique shape forminute size based on a recognition that the shearing strength and thepeeling strength during engaging are extremely low.

Assuming that the engaging element has an ordinary J shape, it isnecessary to set the distance between the lower surface of the distalend of the engaging head and the uppermost point of the engaging head assmall as possible, and to set both the distance between the lowersurface of the distal end of the engaging head and the front surface ofthe substrate sheet, and the distance between adjacent engaging hooks atleast several times larger than the actual size of the companion loops.Consequently, the parameters of the conventional engaging element aredetermined in relation to the size of the companion loops. For example,even when molding the very soft and minute-size engaging elementssuitable for use in paper diaper, it is inevitable to set the curvatureof the engaging head large to secure the necessary engaging strength,and the minimum necessary distance between the lower surface of thedistal end of the engaging head and the front surface of the substratesheet for the loop to enter is determined univocally.

This means that, when securing a predetermined rate of engagement,either the height or density of the engaging element is univocallydecided so that the height cannot be set to a lower value. Therefore,assuming that either the resin material or the hook weight is constant,it is difficult to improve the strength in both the shearing directionand the peeling direction during engagement unless the engaging elementstructure is improved. Also, since the uppermost portion of the engaginghead of the engaging element rising directly from the front surface ofthe substrate sheet is curved, it is impossible to make the touch of theengaging-side surface of the surface fastener smoother, and this curvedtop shape would be a cause for increasing the size of the companion loopand would obstruct the insertion of the engaging head into the loop whenthe loops are to be smaller. Further, even if the whole engaging elementis merely reduced into a minute size, the whole hook-shape engaging headwould inevitably be flexed forwardly or sideways when depressed so thatthe engaging head becomes further unable to engage the companion loops,thus lowering the rate of engagement of the whole surface fastenerconsiderably.

Generally, when making the engaging elements minute in size as mentionedabove, in order to secure adequate softness of the whole surfacefastener, the thickness of the substrate sheet must be reduced. However,if the thickness of the substrate sheet is very small, it tends toextend uniformly or to be easily torn out when the engaging elements ofthe molded surface fastener are separated from the die during continuousmolding, thus causing non-stable molding. Yet if the molding itselfcould be finalized without trouble, the molded substrate sheet wouldbecome wavy or puckered, thus making the molded surface fastener notdurable for practical use.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide a molded surfacefastener which can reliably engage with even minute dense fiber pileloops such as of a non-woven cloth, can secure adequate shearing andpeeling resistance of individual engaging elements during engagement,can improve the touch of the engaging-side surface, can be reduced inheight of engaging elements above one surface of the substrate sheet ascompared to the conventional surface fastener, can prevent engagingheads from extreme lateral and forward bending, can secure a high rateof engagement with the loops of the companion surface fastener, haveadequate durability against repeated loading, and can secure desiredsoftness and tearing strength of the substrate sheet.

According to a first aspect of the invention, these objects areaccomplished by a molded surface fastener comprising: a substrate sheet;and a multiplicity of engaging elements, which constitute a main featureof the surface fastener according to this invention, standing on onesurface of the substrate sheet, each of the engaging elements beingcomposed of a stem rising from the one surface of the substrate sheet,and an engaging head projecting from an upper end of the stem fordetachably engaging a companion loop; the engaging head extending fromthe stem so as to be bent and having a pair of protuberanceshorizontally projecting in opposite directions from opposite side edgesof a top of the engaging head perpendicularly with respect to adirection lengthwise of the engaging head.

In the presence of these protuberances, it is possible firstly to makethe top surfaces of the engaging heads substantially flat to prevent anitchy touch, and secondly to relatively reduce the length from the onesurface of the substrate sheet to an uppermost point of the engaginghead, without changing the length from the one surface of the substratesheet to a lower surface of the engaging head, if the same quantity ofresin is used for the top of the engaging head including theprotuberances.

A third function of these protuberances, unlike the conventionalengaging head having a substantially uniform size in which a companionloop is merely caught with the engaging head curving like a hook, isthat the individual loop of the companion surface fastener can becomewound around the neck between the stem and the protuberances so as notto be easily removed off the engaging head, thus increasing the engagingstrength sharply. Since these protuberances, unlike the conventionalmushroom-type engaging element having an umbrella-shape engaging headextending in all directions from the upper end of the stem, exist onlyon a part of the engaging head extending in one direction of the stem,and allow the loop to smoothly move around the protuberances with aslight frictional resistance, requiring a separating force greater thanthat with the conventional ordinary hook-shape engaging head and smallerthan that with the conventional umbrella-shape engaging head, as theengaging head resiliently deforms to stand up when a peeling force isexerted on the surface fastener. As a result, it is possible to secure arequired degree of engaging strength, instead of the minute size of theengaging heads, without causing any damage to either the engagingelements or the loops.

Further, in the presence of the protuberances, it is possible to modifythe shape of the engaging head. Namely, since the protuberances cause anincreased degree of engaging strength with the loops as mentioned above,it is, possible to bend the whole engaging element into a generallyinverted L-shape with the engaging head extending substantiallystraightway without curving downwardly toward the substrate sheet likethe conventional hook-shape engaging head. This facilitates insertingthe engaging head through even the minute-size loops, such as short andminute single-fiber pile bristling as part of an ordinary non-wovencloth.

For the minute-size and single-fiber pile, it is preferable that theengaging head is inclined by an angle θ with respect to the horizontalplane, the angle θ satisfying a relation -5°≦θ≦+45° and that the top ofthe engaging head is inclined by an angle θ' with respect to thehorizontal plane, the angle θ' satisfying a relation 0<θ'≦+60°. Even ifthe conventional J-shape or mere inverted L-shape engaging elementassumes the above-defined inclined posture, adequate engaging strengthwith the companion loops cannot be realized.

Preferably, the top of the engaging head has a substantially flat topsurface, from which the protuberances horizontally bulge, so that theengaging-side surface of the surface fastener is improved so as todisplay a less itchy touch. Also preferably, the engaging head has ahigher degree of rigidity than the stem so that an adequate rate ofengagement with the companion loops and an adequate degree of peelingresistance can be secured.

Although generally the stem stands upright, at least part of thecircumferential surface of the stem may be inclined with respect to thefront surface of the substrate sheet. Further, each engaging element maybe a single-head structure having a single engaging head extending fromthe stem in one direction, or may be a double-head structure having twoengaging heads branched from the upper end of the stem in a directionperpendicularly to the direction lengthwise f the engaging head, the twoengaging heads extending in two parallel vertical planes in oppositedirections , respectively. The stem may have a width, which isperpendicular with respect to the direction lengthwise of the engaginghead, larger in part than the width of the engaging head. In this case,an uppermost point of the large-width part of the stem may be disposedat a level lower or higher than a extending start point of a lowersurface of the engaging head.

Also preferably, the stem has on its opposite side surfaces a pair ofreinforcing ribs rising from the one surface of the substrate sheet.Each of the reinforcing ribs connects the stems of an adjacent pair ofthe engaging elements mutually confronting perpendicularly with respectto the direction lengthwise of the engaging head. Further, the substratesheet may have at a predetermined number of positions in the one surfacethereof a predetermined number of recesses, from bottom surfaces ofwhich the engaging elements stand, each of the recesses having a widthlarge enough to receive the companion loop. Of course, though thepresence of the recesses allow the engaging elements to be minute, it isnot necessary.

Though these molded surface fasteners may be molded by an ordinaryinjection molding machine, it is preferable that they are continuouslymanufactured in the following method on the following apparatus.

According to this invention, an apparatus for manufacturing a moldedsurface fastener having a substrate sheet and a multiplicity of engagingelements standing on one surface of the substrate sheet, each of theengaging elements being composed of a stem rising from the one surfaceof the substrate sheet, and an engaging head projecting from an upperend of the stem for detachably engaging a companion loop, comprises: adie wheel adapted to be driven for one-way rotation and having in itscircumferential surface a multiplicity of generally L-shapeengaging-element-forming cavities; molten resin supplying means forsupplying molten resin into a predetermined gap between the molten resinsupplying means and the circumferential surface of the die wheel whilethe latter is rotating; cooling means for positively cooling aprimary-primary-intermediate surface fastener attached to acircumferential surface of the die wheel and moving in an arc inresponse to the rotation of the die wheel; and take-up means forcontinuously drawing the primary-primary-intermediate surface fastener,which is solidified while moving in response to the rotation of the diewheel, from the circumferential surface of the die wheel; and heatingand pressing means disposed downstream of the take-up means so as toconfront a path of travel of the top of the engaging head of theprimary-primary-intermediate surface fastener, the top of the engaginghead being heated and pressed from an upper side thereof to form a pairof protuberances bulging from the top of the engaging head transverselyof the top traveling path.

Each engaging-element-forming cavity has a stem-forming cavity openingat the circumferential surface of the die wheel and extending radiallysubstantially toward the axis of the die wheel, and anengaging-head-forming cavity extending circumferentially from an upperend of the stem-forming cavity. The cooling means includes a coolingwater jacket disposed inside the die wheel and a cooling water bathdisposed outside the die wheel for positively cooling part of thecircumferential surface of the die wheel and the molded surfacefastener, which is carried on the circumferential surface of the diewheel and is moving with rotation of the die wheel, from the outer side.Further, the heating and pressing means may be a roller having ahorizontal axis or plate extending perpendicularly to the path of travelof the primary-intermediate surface fastener, and may includetemperature adjusting means and pressure controlling means.

In order to continuously manufacture a molded surface fastener havingthe foregoing structure by said apparatus, molten resin is continuouslyinjected toward the circumferential surface of a rotating die wheel froma continuous injection nozzle under a predetermined resin pressure sothat part of the molten resin is injected into the element-formingcavities of the die wheel, and also is shaped into a substrate sheetalong the circumferential surface of the die wheel to form amultiplicity of engaging elements integral with a substrate sheet. As aresult, a primary-intermediate molded surface fastener is continuouslymolded.

As it is moved along substantially a half of the circumferential surfaceof the die wheel, this primary-primary-intermediate surface fastener ispositively cooled by the cooling water jacket mounted in the die wheeland at the same time, is moved in and through the cooling water bath, inwhich low-temperature cooling water circulates, and is thereby quicklycooled to facilitate solidification. Since the primary-intermediatemolded surface fastener is solidified by this quick cooling beforecrystallization of the molded surface fastener starts, it is possible tomake the whole substrate sheet and all of the engaging elementsadequately soft. Accordingly the molded surface fastener is moresuitable for use in a fastener for underwear, paper diaper, whichrequire an adequate degree of softness.

When the solidified substrate sheet is separated from thecircumferential surface of the die wheel by a pair of take-up rollers,the individual cooled and solidified engaging elements are drawnsuccessively from the engaging-element-forming cavities smoothly as theyresiliently deform into a straight shape. At that time, each of theengaging elements does not perfectly restore to its original shape,assuming a hook-shape posture in which the engaging head slightly risesas compared to the engaging-head-forming cavity.

Especially, if the engaging heads extend in forward and reversedirections with respect to the direction of rotation of the die wheel,the forward engaging head assumes a stand-up posture higher than thereverse engaging head due to the difference of drawing direction.Regarding the posture keeping the shape of the engaging element when theit is drawn off the die wheel before the top is processed with thesubsequent heating and pressing process, the difference of bendingangles of the forward and reverse engaging heads with respect to thestem is reflected directly in the difference of peeling strength. Butafter the heating and pressing process, the difference of bending anglewould be small, while the peeling strength of the forward engaging headwould be particularly increased as compared to the reverse engaginghead.

Namely, the generally inverted L-shape engaging element in which theforward engaging head is deformed more increases considerably in peelingstrength after the protuberances have been formed, as compared to theengaging element in which the reverse engaging head is deformed less inbending angle. With this physical property change in view, if thebending angle of the reverse-engaging-head-forming cavity in thecircumferential surface of the die wheel is previously set to be largerthan that of the forward-engaging-head-forming cavity, it is possible tosecure substantially the same peeling strength for either the engagingelement having the forward engaging head or the engaging element havingthe reverse engaging head.

When a difference in bending angle between theforward-engaging-head-forming cavity and thereverse-engaging-head-forming cavity is to be previously given, thebending angle of the forward-engaging-head-forming cavity is set smallerthan that of the reverse-engaging-head-forming cavity so that theforward and reverse engaging heads drawn from the die wheel assumesubstantially the same angle of inclination with respect to thesubstrate sheet. Preferably, the bending angle of theforward-engaging-head-forming cavity is -5°˜80°, while the bending angleof the reverse-engaging-head-forming cavity is 10°˜90°.

In order not to give a difference in shape between the forward andreverse engaging heads after the heating and pressing process, it isalso preferable to give a difference in length from the opening at thecircumferential surface of the die wheel to a bending start point of theengaging head-forming cavity with respect to the radially extendingstem-forming cavities between the forward- andreverse-engaging-head-forming cavities, in addition to the setting ofthe above-mentioned bending angles. The ratio of the distance betweenthe opening of the stem-forming cavity at the circumferential surface ofthe die wheel and the bending start point of the engaging-head-formingcavity extending in the direction of rotation of the die wheel from thestem-forming cavity, and the distance between the opening of thestem-forming cavity at the circumferential surface of the die wheel andthe bending starting point of the engaging-head-form cavity extendingreversely with respect to the direction of rotation of the die wheelfrom the stem-forming cavity is preferably about 1:1.01˜1:1.50, morepreferably 1:1.15.

After its opposite side edges have been cut off by a trimming unit, thethus primary-intermediate surface fastener is moved through and betweenthe upper and lower rollers serving as the beating and pressing means.During that time the top of the engaging head is heated and pressed bythe upper heating roller, which deforms the top of the engaging head tobend the engaging head slightly toward the downstream side from its topto its distal end and to form a substantially flat top surf ace and apair of transverse protuberances bulging in opposite directions fromopposite sides of the flat top surface. As a result, the molded surfacefastener having on the substrate sheet a multiplicity of engagingelements of the above-mentioned shape is obtained.

The molded surface fastener passed through th e heating and pressingmeans is slowly cooled at normal, ambient temperature, without beingpositively cooled by independent cooling means, whereupon the cooledsurface fastener is wound up in a roll to finalize the manufacturing.When the heated and deformed top of the engaging head is slowly cooledto become solidified, crystallization in the heated portion proceeds sothat the engaging head would increase in rigidness as compared to thestem. Specifically, since the engaging heads have an increased degree ofrigidness as compared to the substrate sheet and the engaging elements,which are quickly cooled to retard crystallization and hence to becomeexcellent in softness, it is possible to secure adequate rigidness ofthe engaging heads, even though the engaging elements are minute in sizeand very high in softness, thus guaranteeing a required degree ofstrength in the peeling direction, even with a single-head--structureengaging element.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary side view of a molded surface fastener accordingto a first structural example of this invention;

FIG. 2 is a plan view of the molded surface fastener of the firststructural example;

FIG. 3 is a front view of the molded surface fastener of the firststructural example;

FIGS. 4A and 4B are fragmentary side and front views of a modificationof the molded surface fastener of the first structural example;

FIG. 5 is a fragmentary side view of a molded surface fastener accordingto a second structural example of the invention;

FIG. 6 is a plan view of the molded surface fastener of the secondstructural example;

FIG. 7 is a front view of the molded surface fastener of the secondstructural example;

FIGS. 8A and 8B are fragmentary side and front views of a modificationof the molded surface fastener of the second structural example;

FIG. 9 is a side view of another modification of the molded surfacefastener of the second structural example;

FIG. 10 is a front view of the last-mentioned modified molded surfacefastener of the second structural example;

FIG. 11 is a perspective view, partly in cross section, of an injectionmolding die for use in manufacturing the molded surface fastener;

FIG. 12 is a fragmentary exploded perspective view showing, on anenlarged scale, an example of internal shape of anengaging-element-forming cavity;

FIG. 13 is a general view showing a schematic structure of an apparatusfor continuously manufacturing the molded surface fastener using aninjection nozzle;

FIG. 14 is an enlarged cross-sectional view schematically showing aprimary-intermediate surface fastener molding station of the apparatus;

FIG. 15 is an exploded perspective view showing an example of cavitiesof a die wheel used in the apparatus;

FIG. 16 shows the manner in which an engaging head is processed byheating and pressing means, which is a characterizing part of thisinvention;

FIGS. 17A and 17B are fragmentary side views showing the respectiveshapes of examples of forward and reverse engaging elements, before theheating and pressing process, which have a forward engaging headextending in the direction of rotation of the die wheel and a reverseengaging head extending reversely with respect to the direction ofrotation of the die wheel;

FIGS. 18A and 18B are fragmentary side views showing the respectiveshapes of the forward and reverse engaging elements after the heatingand pressing process;

FIG. 19 is a graph showing the results of peeling strength tests of themolded surface fastener before and after the heating and pressingprocess;

FIG. 20 is a perspective view showing a preferable example of shape ofan engaging-element-forming cavity;

FIG. 21 is a view showing a schematic structure of an apparatus forcontinuously manufacturing the molded surface fastener using aprotuberance forming station according to a second embodiment of theapparatus of the invention; and

FIG. 22 is a view showing a schematic structure of an apparatus forcontinuously manufacturing the molded surface fastener using a modifiedprotuberance forming station according to a third embodiment of theapparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of this invention will now be described in detailwith reference to the accompanying drawings. FIG. 1 is a fragmentaryside view of a molded surface fastener having a first structural exampleof engaging elements, which is a typical one of this invention, FIG. 2is a plan view of the molded surface fastener of the first structuralexample, and FIG. 3 is a front view of the molded surface fastener ofthe first structural example.

As shown in FIGS. 1 through 3, the molded surface fastener comprises asubstrate sheet 1, and a multiplicity of inverted L-shape engagingelements 2 standing on a front surface of the substrate sheet 1. In theillustrated example, engaging heads 22 of the engaging elements 2 in thesame row extend in the same direction, while engaging heads 22 of theengaging elements 2 in each adjacent pair of rows extend in oppositedirections. The individual engaging elements 2 of every row areidentical in structure, and the substrate sheet 1 has the same structureat each and every row of the engaging elements 2; therefore thefollowing description of the surface fastener SF is limited to itspartial structure.

The substrate sheet 1 has in the front surface a predetermined number ofcontinuous straight recesses 1a, from bottom surfaces of which amultiplicity of the engaging elements 2 stand at a predetermined pitchwith their engaging head 22 extending in the same direction. Each of theengaging elements 2 has a stem 21 standing from the bottom surface ofeach recess la and the engaging head 22 bending and standing from anupper end of the stem 21 in an engaging-element-row direction. Further,according to the illustrated example, the engaging heads 22 in eachadjacent pair of rows of the engaging elements 2 extend in oppositedirections. The recess 1a is not limited to the aforementioned shape,but alternatively, the recesses 1a along each engaging element row maybe disposed perfectly independently of one another. In anotheralternative form, the individual recess sections 1a along each adjacentpair of engaging element rows may be arranged in a staggering pattern onthe front surface of the substrate sheet 1; in such case, if areinforcing rib 23 (described later) projecting, from the front surfaceof the substrate sheet 1, on one side of an intermediate portion betweeneach pair of front and rear engaging elements 2 in one row is omitted,in spite of improving the softness of the substrate sheet, it ispossible to secure a predetermined degree of tearing strength.

In the surface fastener SF of this embodiment having such a basicstructure, though the distance H between the lower surface of the distalend of the engaging head 22 and the base end (bottom surface of therecess 1a) of the stem 21 is the same as conventional, the distance H'between the lower surface of the distal end of the engaging head 22 andthe recessfree area of the front surface of the substrate sheet 1 isequal to the difference between the distance H, which is related to theactual height of the engaging element 2, and the depth of the recess 1a.This means that though the actual height H of the engaging element 2standing on the substrate sheet 1 is the same as conventional, theapparent height H' of the engaging element 2 above the front surface ofthe substrate sheet 1 is shorter than the actual height H by the depthof the recess 1a. Having these recesses 1a in its front surface, thesubstrate sheet 1 can be improved remarkably in softness though itsapparent thickness is the same as convention. Also this substrate sheet1 can be kept from excessive expansion or ripping when the surfacefastener SF is peeled off the die after molding. As a result, a highquality product free of puckering in the substrate sheet 1 andadequately durable for practical use can be obtained.

Further, when the engaging element 2 of the surface fastener SF of thisembodiment having the aforementioned structure engages the companionloop 3, the distal end of the loop 3 comes under the engaging head 22 asguided by the recess 1a to reach the base end of the stem 21 of theengaging element 2 so that the engaging head 22 is inserted through theloop 3 smoothly.

Regarding the parameters of the illustrated example, the depth of theindividual recesses 1a of the substrate sheet 1 is about 0.05 mm, andits width is equal to that of the stem 21. Accordingly, the base end ofthe engaging element 2 is disposed on the bottom surface of theindividual recess 1a, and the upper portion of the engaging element 2from a point, 0.05 mm high, of the stem 21 to the top 22a of theengaging head 22 projects above the front surface of the substrate sheet1.

In this embodiment, the actual height H of the engaging element 2 abovethe bottom surface of the recess 1a is about 0.35 mm, while the apparentheight H' of the engaging element 2 above the front surface of thesubstrate sheet 1 is 0.30 mm. The width of the stem 21 in a directionperpendicular to the engaging element row is 0.15 mm equal to the widthof the engaging head 22 in the same direction. Further, the thickness ofthe substrate sheet is 0.30. mm, and on the front surface of thesubstrate sheet 1, the engaging elements 2 are arranged at a pitch of0.8 mm along each engaging element row and are spaced a distance of 0.45mm from those of adjacent engaging element rows. These values, which areshown only as an optimum example, should by no means be limited to theillustrated example and may be changed variously as desired in relationto the companion loops.

As a characteristic feature of the engaging element 2 according to thisinvention, a whole top 22a of the engaging head 22 defines asubstantially oval flat surface having a pair of protuberances 22a'horizontally bulging in opposite directions from opposite sides of theengaging head 22, as viewed from the upper side in FIG. 2. A longerdiameter of the oval extends longitudinally of the engaging head 22,while a shorter diameter extends transversely of the engaging head 22.In this embodiment, the length of each of the protuberances 22a' isabout 0.10 mm, and the total width of the top 22a of the engaging head22 in a direction transverse of the engaging element row is 0.25, whichis 0.05 mm larger than the width of either the remaining part of theengaging head 22 or the stem 21. The presence of the protuberances 22a'displays the following various useful functions, which could not beexpected from the conventional engaging heads.

For a first function, it is possible to define a substantially flatsurface on the top 22a of the engaging head 22, giving a less itchytouch , or smoother hand to the surface fastener. For a second function,assuming that the quantity of resin for the top 22a a of the engaginghead 22 including the protuberances 22a' is the same as conventional, itis possible to make the apparent height of the engaging head 22 from thefront surface of the substrate sheet 1 to a top point thereof relativelyshorter without changing the height of the engaging head 22 above thefront surface of the substrate sheet 1. Therefore, it is possible notonly to make the engaging elements 2 minute but also to leave the frontsurface of the substrate sheet 1 merely flat, as shown in FIGS. 4A and4B, without forming any recesses of FIGS. 1 through 3.

For a third function, these protuberances 22a' has, not only thefunction of merely engaging loops with the conventional engaging headhaving a substantially uniform size, but a function that the individualloop 3 of the companion surface fastener can be caught with rear ends22a'-1 of the protuberances 22a' so as not to be easily removed off theengaging head 22, thus increasing the engaging strength sharply. Sincethese protuberances 22a', unlike the conventional mushroom-type engagingelement having an umbrella-shape engaging head extending in alldirections from the upper end of the stem 21, exist only on a part ofthe engaging head 22 extending in one direction of the stem 21, andallow the loop 3 to smoothly move around the protuberances 22a', thoughthe loop 3 is caught by the rear ends 22a'-1 of the oppositeprotuberances 22a' of the engaging head 22 extending substantially in astraight line as mentioned above, as the engaging head 22 resilientlydeforms to stand up when a peeling force is exerted on the surfacefastener, thus achieving smooth separation. So, the separation can beachieved by a separating force greater than that with the conventionalordinary hook-shape engaging head and smaller than that with theconventional umbrella-shape engaging head. As a result, it is possibleto secure a required degree of engaging strength, in spite of the minutesize of the engaging heads 22, without causing any damage to either theengaging elements 2 or the loops 3, in spite of such a minute size.

Further, in the presence of the protuberances 22a', it is possible tomodify the shape of the engaging head 22. Namely, since theprotuberances 22a' cause an increased degree of engaging strength withthe loops as mentioned above, it is possible to bend the whole engagingelement 2 into a generally inverted L shape with the engaging head 22extending substantially straightway without curving downwardly towardthe substrate sheet 1 like the conventional hook-shape engaging head.This facilitates inserting the engaging head 22 into the companion loop,which is even of a minute size, such as short and minute single-fiberpile bristling as part of an ordinary non-woven cloth.

Of course, this invention includes other shapes, the entire shape of theengaging head 22, which is closely akin to the ordinary shape having thecurved shape in which the distal end is slightly curved toward the frontsurface of the substrate sheet. However, for the minute-size andsingle-fiber pile, in the case that the vertical thickness of theengaging head 22 is uniform, it is preferable that the shape of the topof each engaging head 22 extends straightly and that the engaging head22 is inclined with respect to a plane parallel to the front surface ofthe substrate sheet 1, i.e. the horizontal plane, by an angle θ of-5°˜+45°, preferably by an angle θ of +10°˜+30°. Further, the lowersurface of the engaging head 22 is inclined by an angle θ' of 0°˜+60°with respect to the front surface of the substrate sheet 1 in order tofacilitate insertion of the engaging head 22 into the minute-size andsingle-fiber pile. Even with such a structure, it is impossible toobtain an adequate engaging strength with respect to the companion loops3. With the conventional J-shape or mere inverted L-shape engaging head,as long as it is a single head, such an adequate engaging strength couldnot be expected, which is apparent from, for example, Japanese PatentLaid-Open Publication No. Hei 2-5847 (U.S. Pat. No. 4,884,060).

Also preferably, the stem 21 has on its opposite side surfaces a pair ofreinforcing ribs 23 rising from the front surface of the substrate sheet1, forming a line perpendicular to the direction of the engaging elementrows. Each of the reinforcing ribs 23 connects side surfaces of thestems 21 of an adjacent pair of the engaging elements 2. Of course, eachreinforcing rib 23 may project from the side surface of the stem of eachengaging element 2 independently of one another. Further, the shape ofthe reinforcing rib 23, its height above the front surface of thesubstrate sheet 1. and its width in the direction of the engagingelement row may be set as desired. For example, if at least one of thefront and rear surfaces of the stem 21 is inclined with respect to thevertical plane, the reinforcing rib 23 may rise beyond the inclinedsurface in parallel to the center line of the stem 2 and terminates inan apex substantially equal in height to the uppermost point of theengaging head 22 or short of the uppermost point of the engaging head 22along an axis of the engaging element 2. The reinforcing ribs 23 serveto assist in increasing the rigidity of especially the minute-size stem21. Further, if each adjacent pair of engaging elements 2 of eachengaging element row are connected by the reinforcing rib 23 as in thisembodiment, it is possible to effectively prevent the substrate sheet 1from being torn either longitudinally or transversely of the engagingelement rows.

FIGS. 5 through 7 shows modified engaging elements 2 according to asecond structural example of this invention. According to the secondstructural example, each mutually oppositely directed pair of engagingelements 2 in an adjacent pair of engaging element rows in the firstembodiment are joined together at their confronting side surfaces in acomposite or double-head structure. This composite engaging element 2has two engaging heads 22 on a single stem 21. In this double-headstructure, the two straightly extending engaging heads 22, each havingthe same shape as that of the first embodiment, are branched in oppositedirections from the upper end of the single stem 21 along of theengaging element rows by dividing the upper end of the stem 21transversely of the engaging element rows.

Accordingly, in this embodiment, if the same quantity of resin as in thefirst embodiment is used for the engaging elements 2, the two engagingheads 22 each having a common width of that of the first embodimentproject in opposite directions from the upper end of the single stem 21and extend in two parallel vertical planes. Therefore, with thedouble-head structure, it was discovered that it is possible to increasethe density of the engaging heads 22 substantially double as compared tothe first embodiment, without increasing the density of the engagingelements 2, so that the rate of engagement with the companion loops 3also would necessarily increase.

Further, in this case, each composite engaging element 2 includes alarge-width portion 21a rising from the base of the stem 21 continuouslyto each engaging head 22 and having a double thickness as compared tothe engaging head 22. This means that if the quantity of resin for eachsubdivided engaging head 22 is equal to the resin quantity for thesingle engaging head 22 of the first embodiment, i.e. each of thesub-divided engaging heads 22 have an identical shape with the sameparameters as that shown in FIGS. 1 through 3, a double quantity ofresin is used for part of the stem 21 as compared to the single engaginghead 22 of the first embodiment, thus causing an increased degree ofrigidity of the large-width portion 21a of the stem 21. Further, if thedouble-head engaging element 2 of this embodiment has a pair ofreinforcing ribs 23 integrally formed on opposite side surfaces of thestem 21, it is possible to reduce the rate of falling flat of theengaging elements 2 remarkably to thereby realize reliable engagementwith and separation from the companion loops 3.

In the second structural example of the engaging element 2 shown inFIGS. 5 through 7, the diverging point of the two engaging heads 22,which can be shown from a side of the engaging element 2, is disposed ata level higher than the lower surface of the engaging head 22. Theheight of the diverging point may be set as desired; for example, thetwo engaging heads 22 may be branched halfway of the stem 21 as shown inFIG. 8A and 8B at a position lower than the lower surface of theengaging head 22.

FIGS. 9 and 10 show a modification of the double-head engaging element 2of the second structural example. This modification is differentiatedfrom the second structural example by a generally trapezoidallarge-thickness portion 21a spanning over the entire width and risingfrom the front surface of the substrate sheet 1 to the diverging pointof the two engaging heads 22. With this trapezoidal large-thicknessportion, it is possible to secure an increased degree of rigidity at thebase or lower portion of the stem 21, without impairing the softness atthe upper portion of the stem 21, so that the base portion of the stem21 can be kept free from easy bending, thus securing adequate rate ofengagement with the companion loops 3.

Though there is no illustration in the drawings, a pair of engagingheads 22 each having a width equal to the width of the single stem 22may extend in opposite directions in a common vertical plane, as long asthe single stem 21 has adequate rigidity even by itself.

The molded surface fastener SF of this invention having such a structuremay be manufactured either batchwise using the ordinary injectionmolding machine or may be continuously using the apparatus disclosed in,for example, U.S. Pat. Nos. 4,984,339 and 5,441,687.

FIG. 11 schematically shows an injection molding die for the surfacefastener SF, and FIG. 12 shows, on an enlarged scale, an example of aninternal shape of the molding cavity for the individual engagingelement. The remaining parts of the injection molding machine areidentical with those of the same-type conventional injection moldingmachine, so the following description is limited to the molding die andthe engaging-element-forming cavities.

In FIG. 11, reference numeral 4 designates an injection molding moldcomposed of a movable die part 41 and a fixed die 42. When the moldingmold 4, is closed, the peripheral parting surface of the movable diepart 4 is brought into contact with the peripheral parting surface ofthe fixed die 42 and, at the same time, an engaging-element-formingpattern 43 of the movable die 41 is placed into the fixed die part 42 todefine a substrate-sheet-forming gap between a flat cavity surface ofthe fixed die 42 and the engaging-element-forming pattern 43 of themovable die 41. The engaging-element-forming pattern 43 is composed of anumber of different plates 43a-43c, which are placed in close contactone over another to define a multiplicity of engaging-element-formingcavities 44. With the plates 43a-43c placed in close contact with oneanother, the movable die 41 is moved toward and away from the fixed die42 to close and open the mold 4; when the die 4 is opened, theindividual plates 43a-43c are separable from one another.

Of the plates 43a-43c, the central plate 43b has a multiplicity ofengaging-element-forming cavities 44b each for forming the stem 21 andthe engaging head 22 of the engaging element 2, while each of adjacenttwo plates 43a, 43c has a protuberance-forming cavity 44a' for forming arespective one of the two protuberances 22a' forming a part of the top22a of the engaging head 22, and a reinforcing-rib-forming cavity 44cfor forming a respective one of the two reinforcing rib 23. According tothe illustrated example, the protuberance-forming cavity 44a is a recesswhose contour is a half of an oval divided into halves along the longdiameter. When these three plates 43a-43c are placed in close contactone over another, a multiplicity of engaging-element-forming cavities 44are defined in the engaging-element-forming pattern 43 of the movabledie part 41, whereupon molten resin 60 is injected into the cavities 44from an injection nozzle 45. Thus a molded surface fastener SF having amultiplicity of engaging elements 2 on a substrate sheet 1 as shown inFIGS. 4A and 4B if molded

FIG. 13 schematically shows an general structure of an apparatus forcontinuously molding the surface fastener SF of this invention, and FIG.14 shows, on an enlarged scale, a molding station of the apparatus. InFIGS. 13 and 14, reference numeral 6 is an injection nozzle, whose tiphas an arcuate surface complementing the circumferential surface of adie wheel 5 (described later), for continuously injecting molten resinfrom an orifice 6a. The injection nozzle 6 is a T-type die disposed in aconfronting relation to the circumferential surface of the die wheel 5with a gap corresponding to the thickness of the substrate sheet 1, anda constant quantity of molten resin 60 is continuously injected in asheet form from the orifice 6a at a predetermined resin pressure. Inthis embodiment, the injection nozzle 6 has a single central sprue 6b.The molten synthetic resin 60 is examplified by polypropylene,low-density polyethylene (LDDE), polyester elastomer, or nylon.

A circumferential surface of the die wheel 5 serves as a molding surfacefor molding the surface fastener SF. As described above, the gap isprovided between the top arcuate surface of the injection nozzle 6 andthe die wheel 5 with the axis of the die wheel 5 being parallel to theorifice 6a. The die wheel 5 is a hollow drum having a water-coolingjacket 7a inside and composed of a multiplicity of non-illustratedring-shape plates fixedly placed one over another along its axis in alaminate form, as shown in FIG. 14.

In this embodiment, as shown in FIG. 14, the die wheal 5 has amultiplicity of engaging-element-forming elements 51 in rows extendingaround its circumferential surface and spaced at a predetermined pitchin a direction parallel to the axis of rotation of the die wheel 5.Between each adjacent pair of rows of engaging-element-forming cavities51, there is a ring-shape recess 51d forming around the circumferentialsurface of the die wheel 5 and having a depth of Dh and a multiplicityof generally triangular reinforcing-rib-forming cavities 51c having adepth larger than that of the recess 51d and arranged in alignment ofthe engaging-element-forming cavities 51c in a direction parallel to theaxis of rotation of the die wheel 5. The ring-shape recess 51d defines acavity for forming part of the front surface of the substrate sheet 1.Each of the engaging-element-forming cavities 51 is composed of astem-forming cavity 51a extending from the circumferential surface ofthe die wheel 5, an engaging head-forming cavity 51b extendingstraightly from an end of the stem-forming cavity 51a and inclined by anangle 85° with respect to the stem-forming cavity 51a.

The die wheel 5 having such a structure is driven by a non-illustratedknown drive unit for rotation in the direction of an arrow shown in FIG.14. The bending angle of the engaging-head-forming cavity 51b withrespect to the stemforming cavity 51a is determined with estimation ofthe deformation of the engaging head 22 when the top 22a of the engaginghead 22 is heated and depressed from the upper side by heating andpressing means 8 (described later).

Also in this embodiment, a substantially lower part of the die wheel 5is dipped in a cooling water bath 7b disposed under the die wheel 5. Apair of take-up rollers 10, 11 are disposed downstream and diagonallyupwardly of the cooling water bath 7b. A trimming unit 12 also isdisposed further downstream of the take-up rollers 10, 11 for cuttingedges of a primary-intermediate molded surface fastener SF', which isthe blank of a final-product molded surface fastener SF. Furtherdownstream of the trimming unit 12, a vertical pair of heating andpressing rollers 8a, 8b constituting a heating and pressing means, whichis the most characteristic part of this invention, for forming theprotuberances 23a' of the engaging head 22. Disposed at a positionbetween the trimming unit 12 and the heating and pressing rollers 8a,8b, is a tension control unit 13 for adjusting the tension of theprimary-intermediate molded surface fastener SF'.

Inside the upper roller 8a, a non-illustrated heating source is disposedso that the surface temperature of the roller 8a is set at a resinsoftening temperature. Further, the lower end of the circumferentialsurface of the upper roller 8a is disposed at a Level slightly below ahorizontal plane passing the engaging head 22' of theprimary-intermediate molded surface fastener SF', as shown in FIG. 16 ona large scale. The setup position of the upper roller 8a is determinedaccording to a desired size of the protuberances 22a' bulging from thetop 22a of the engaging head 22 of the engaging element 2 according tothe invention. On the other hand, the upper surface of the lower roller8b is disposed in a horizontal plane in which the rear surface of thesubstrate sheet 1 of the primary-intermediate surface fastener SF'travels. In this case, as shown in FIG. 13, the vertical position of theupper roller 8a can be adjusted by a known roller-level adjuster 9a(FIG. 13), and the heating temperature of the upper roller 8a can beadjusted as desired according to the kind of the resin by a knowntemperature control unit 9b (FIG. 13). Although both the upper and lowerrollers 8a, 8b may be positively driven for rotation in synchronism witheach other, at least the upper roller 8a is operatively connected to adrive source such as a non-illustrated electric motor for rotation. Thelower roller 8b may be substituted by a table having a less frictionalflat top surface.

The experiments conducted under the direction of the present inventorsshow that when the individual cooled and solidified engaging elements 2are drawn successively off the generally inverted L-shapeengaging-element-forming cavities 51, in which the individual engaginghead-forming cavities 51a extend from the corresponding stem-formingcavities 51b in a direction of the rotation of the die wheel 5 or in itsreverse direction, degrees of deformation of the engaging elements 2drawn from the cavities 51 having the direction of the die wheel'srotation and drawn from those having the reverse direction are differentto a large extent.

FIG. 17 A and 17B shown the differential of the degrees of deformation,in which the arrows indicates the rotating direction of the die wheel 5.As shown in FIGS. 17A and 17B, the engaging head 22' extending in therotating direction of the die wheel 5 (hereinafter called the forwardengaging head ) assumes a stand-up posture higher than the engaging head22' extending in the reverse direction of rotation of the die wheel 5(hereinafter called the reverse engaging head), and does not restore itsoriginal shape enough after having been drawn from the cavity 51, sothat the degree of its bending with respect to the stem 21' is toolittle and its bending angle is necessarily large. Consequently, inorder to match the bending angle of the forward engaging head 22' withthat of the reverse engaging head 22', it is necessary to previously setthe bending angle of the forward engaging-element-forming cavity 51different from that of the reverse engaging-element-forming cavity 51 inthe circumferential surface of the die wheel 5.

For molding the surface fastener SF of this invention by the apparatusfor manufacturing a surface fastener having the above-mentionedstructure, molten resin 60 is continuously injected from the injectionnozzle 6 into the gap, which is defined between the rotating die wheel 5and the orifice 6a, under a predetermined resin pressure, part of themolten resin 60 fills the gap to mold the substrate sheet 1' and, at thesame time, the remaining part of the molten resin 60 fills successivelythe engaging-element-forming cavities 51, which are formed in thecircumferential surface of the die wheel 5, to mold a multiplicityengaging element blanks 2' integrally on the front surface of thesubstrate sheet 1' along the rotation of the die wheel 5. Thus theprimary-intermediate molded surface fastener SF' is continuously molded.

While the primary-intermediate molded surface fastener SF', which is theblank of the surface fastener SF of the invention, is moved along asubstantially half part of the circumferential surface of the die wheel5, this primary-intermediate surface fastener SF' is positively cooledby the cooling water jacket 7a mounted in the die wheel 5 and, at thesame time, the primary-intermediate surface fastener SF' is moved in andthrough the cooling water bath 7b, in which low-temperature (about 15°C.) cooling water circulates, and is thereby quickly cooled tofacilitate solidification. Since the primary-intermediate molded surfacefastener SF' is solidified by this quick cooling before crystallizationof the molded surface fastener SF' starts, it is possible to make thewhole substrate sheet 1 and all of the engaging elements 2 adequatelysoft.

When the solidified substrate sheet 1' is separated from thecircumferential surface of the die wheel 5 by the takeup rollers 10, 11,the individual cooled and solidified engaging elements 2' are drawnsuccessively off the engaging element-forming cavities 51 smoothly asthey resiliently deform into a straight shape. At that time, theengaging elements 2' tend to restore to the original shape but docompletely, and an individual engaging head 22' has such a shape thatthe engaging head 22' stands from at a bending angle slightly upwardlycompared to the invented L-shape of the engaging element-formingcavities 51 .

In this embodiment, the primary-intermediate surface fastener SF' isseparated off the die wheel 5 using the upper and lower take-up rollers10, 11 rotating in opposite directions in synchronism with each other.Although the circumferential surfaces of the take-up rollers 10, 11 maybe smooth, it is preferable to provide each of them with a ring-shapegroove on a circumferential portion thereof where the engaging elementrow processes so as not to damage the engagingelements 2. Theprimary-intermediate molded surface fastener SF' is moved through thetrimming unit 12, in which opposite side edges of the molded surfacefastener .SF' are cut off, and then through and between the upper andlower rollers 8a, 8b constituting a heating and pressing means 8. Whiletraveling through the heating and pressing means 8, the top portion ofthe engaging heads 22' of the engaging element 2' are heated and pressedby the upper heating roller 8a so that the individual engaging head 22'is inclined slightly forwardly from its base end and to its, distalends, as indicated by the solid line in the claming at the same time,deforms as softened from its top, as shown in FIG. 16. As a result, thetop 22a (indicated in dotted lines in FIG. 1) of the engaging head 22'is shaped so as to have a substantially flat top surface P and a pair ofopposite side protuberances 22a' (indicated solid lines in FIGS. 1through 3). The flat top surface P may be slightly depressed at itscentral area due to the subsequent cooling, depending on the moldingconditions.

In this invention, the molded surface fastener SF having passed throughthe heating means 8 is slowly cooled at normal temperature without usingseparate cooling means, whereupon the molded surface fastener SF iswound up in a roll to finalize the manufacturing. In this invention, itis important to heat and press the top of the engaging element 2 and toslowly cool the top 22a including the protuberances 22a'. Namely, whilethe heated top 22a of the engaging head 22 softened by being heated anddeformed by pressing is cooled slowly, the heated portion becomescrystallized to have an increased degree of rigidness as compared to thestem 21

Since only the engaging head 22' has a high degree of rigidness ascompared to the substrate sheet 1' and the majority of the engagingelement 2', it is possible to secure adequate resistance against peelingfrom the companion loops, though the engaging elements 2 are minute insize and very high in softness, as the rigidity of the engaging heads 23is secured. On the other hand, since a strength of a treating directionof the substrate sheet 1, can be secured in the case that the stem 21has a pair of reinforcing ribs 23 on its opposite surface even if theengaging element 2 has a single head as in this invention, the resultingmolded surface fastener SF is a high quality product having a less itchytouch on its engaging surface and an adequate degree of engagingstrength, though excellent in softness and minute in size but rigid atthe engaging head 22, guaranteeing good durability for repeated use.FIG. 19 is a graph in which the peeling strength of the engaging element2 having processed with the heating and pressing process is comparedwith that of the unprocessed engaging element 2' right after having beendrawn of f the die wheel 5 and before having been processed with theheating and pressing process. Given that after the top 22a of theengaging head 22 has been heated and pressed, it is understood from thisgraph that the peeling strength of the engaging element 2 has an sharplyincreased degree of peeling strength as compared to the unprocessedengaging element 2'.

According to the embodiments of this invention in which the engagingelement 2 has a substantially invented 2 shape, when the engagingelement 2' drawn off the die wheel 5 does not restore to its originalshape, which is that of the individual L-shape engaging-element-formingcavity 51, and assumes an increased angle of bending as compared to thatof the engaging-element-forming cavity 51, as shown in FIGS. 17A and17B. Further, because of its greater resistance when drawing from thecorresponding cavity 51, the forward engaging head 22' of FIG. 17B islarger in angle of bending than the reverse engaging head 22' of FIG.17A.

In the experiments of the present inventors, a discovery was made thatthe difference in restoration of shape after drawing from the die wheel5 is reflected interestingly on the physical property of the engagingelement 2 after being processed to form the protuberances 22a', as shownin FIG. 19. According to the graph of FIG. 19, in the shape of theengaging element 2' before the heating and pressing process as shown inFIGS. 17A and 17B, the difference in angle of bending between theforward and reverse engaging heads 22' is directly reflected on thedifference in peeling strength between the forward and reverse engagingheads 22'. In the engaging element 2 after the heating and pressingprocess as shown in FIGS. 18A and 18B, the difference in angle ofbending between the forward and reverse engaging heads 22 is reduced,and the peeling strength of the forward engaging head 22 is increasedsharply as compared to that of the reverse engaging head 22.

Namely, the generally inverted L-shape engaging element 2 in which theforward engaging head 22' is deformed more increases sharply in peelingstrength after the protuberances 22a' have been formed, as compared tothe engaging element 2 in which the reverse engaging head 22' isdeformed less in angle of bending. With this physical property change inview, if the angle of bending of the individualreverse-engaging-head-forming cavity 51 in the circumferential surfaceof the die wheel 5 is previously set to be larger than that of theindividual forward-engaging-head-forming cavity 51, it is possible tosecure substantially the same peeling strength for either the engagingelement 2 having the forward engaging head 22' or the engaging element 2having the reverse engaging head 22'.

FIG. 20 schematically shows in the same plate a preferred shape ofengaging-element-forming cavity 51 in which a difference is previouslyset between the angle α1 of bending of the forward-engaging-head-formingcavity 51b and the angle α2 of bending of thereverse-engaging-head-forming cavity. In order not to give a differencein shape between the tops 22a the forward and reverse engaging heads 22after the heating and pressing process, it is preferable that. inaddition to the setting of the different bending angles α1 and α2, adifference is given between a depth h1 of the bending start point 0 ofthe forward-engaging-head- forming cavity 51b with respect to thecorresponding stem-forming cavity 51a standing from the opening of thecircumferential surface of the die wheel 5 in its radius direction and adepth h2 of the bending start point 0 of thereverse-engaging-head-forming cavity 5b with respect to thecorresponding stem-forming cavity 51a. Preferably, the angle α1 ofbending of the forward-engaging head-forming cavity 51b is -5°˜+80°while the angle α2 of bending of the reverse-engaging-head-formingcavity 51b is +10°˜-+90°. The ratio of the depths h1 and h2 ispreferably about 1:1.01-1:1.50. Of course, these bending angles anddepth ratios depend on the substance of the resin to be used andtherefore should by no means be limited to particular numeral values buttend be approximated to the illustrated numeral values.

In the illustrated numeral examples, the angle α1 of bending of theforward engaging-element-forming cavity 51 is 10 the depth h1 of thestem-forming cavity 51a of the forward-engaging-element-forming cavity51 is 0.20 mm, the angle α2 of bending of thereserve-engaging-element-forming cavity 51 is 27°, and the depth h2 ofthe stem-forming cavity 51a of the reverse-engaging-element-formingcavity 51 is 0.23 mm.

FIG. 21 is a vertical cross-sectional view of. an apparatus forcontinuously manufacturing the molded surface fastener using a modifiedform of heating and pressing means 8. This embodiment is substantiallyidentical in entire construction with the foregoing embodiment exceptthe protuberance forming station. In this illustrated example, upper andlower plates 8c, 8d are used as the heating and pressing means 8. Theupper plate 8c has a non-illustrated heating source heater and canthereby be heated up to a resin softening temperature, and the verticalposition of the upper plate 8c can be adjusted by a non-illustratedvertical-position adjuster. The lower plate 8d is fixed in such a mannerthat its upper surface is positioned in alignment with the path oftravel of the primary-intermediate surface fastener SF'. The upper plate8c is disposed at a level slightly lower than the plane in which theengaging head 22' of he engaging element 2' of the primary-intermediatesurface fastener SF' travels. This setup position is decided by anestimated length of the opposite protuberances 22a' bulging from the top22a of the engaging head 22 of the engaging element 2 according to thisinvention.

According to this embodiment having the foregoing structure, after theprimary-intermediate surface fastener SF' continuously molded on anon-illustrated die wheel in rotation is moved arcuately with rotationof the die wheel, it is continuously separated from the circumferentialsurface of the die wheel as positively drawn by the take-up rollers 10,11. As it is moved arcuately with the die wheel, this primaryintermediate surface fastener SF' is quickly cooled by a non-illustratedcooling water jacket mounted in the die wheel and a non-illustratedcooling water bath disposed under the die wheel. This quicksolidification makes the primary-intermediate surface fastener SF' highin softness.

After opposite edges of the primary-intermediate surface fastener SF'have been cut off by a non-illustrated trimming unit, the thus moldedprimary-intermediate surface fastener SF' is moved through and betweenthe upper and lower plates 8c, 8d serving as the heating and pressingmeans. During that time, the top 22a of the engaging head 22, which isindicated by dotted lines in FIG. 8. is heated and pressed by the upperheating plate 8c, and the engaging element 2 deforms to bend slightlytoward the downstream side from its line to distal end as indicated by asolid lines in FIG. 8. Further, the top 22a deforms as softened from itsupper point to form a pair of transverse protuberances 22a' bulging inopposite directions from opposite sides of the flat top surface and isslowly cooled and solidified, as in the previous embodiment, as aresult, the rigidity of the protuberances 22a' and the circumferentialportions thereof increases, so that ideal engaging elements 2 having thesame shape and function as those of the first structural example areobtained.

FIG. 22 is an overall view schematically showing a structure of ananother apparatus for continuously manufacturing the molded surfacefastener using a modified protuberance forming station. This embodimentis differentiated from the first and second embodiments in that theindividual engaging-element-forming cavity 510 extends substantiallymerely straightway and is slightly inclined with respect to a radialdirection a die wheel 5, not assuming a substantially inverted L shape.The basic structure of the remaining units or devices of the embodimentis identical with the second embodiment except that an upper heatingplate 80c and a lower water tank 80d are used as heating and pressingmeans 80.

Since each of the engaging elements 2' standing in an inclined postureon the substrate sheet 1' of the primary intermediate surface fastenerSF' is merely substantially straight, the height of the inlet end of theupstream part 80c-1 of the upper plate 80c is set at the same level asthat of the upper end of the engaging element 2'. Further, the distancebetween the bottom surface of the upper plate 80c and water level in thelower water bath 80d is made so as to gradually decreases toward acentral position of the upper plate 80c along a path of travel of thesurface fastener SF' and to be uniform along the downstream part 80c-2.When it travels along the upstream part 80c-1 of the upper plate 80c,the substantially straight engaging head 22' is bent by the upper plate80c; then when it travels along the downstream part 80c-2 of the upperplate 80c, the top 22a of the bent engaging head 22' is gradually heatedand pressed by the upper plate 80c to form a pair of protuberancesbulging in opposite directions from opposite side edges of the top 22a.Though the upper plate 80c is necessarily heated, the engaging head 22'would be bent too quickly, and also its quality would be deteriorated ifthe upstream part 80c-1 is heated at high temperature. In order to avoidthe overheating, the temperature of the upstream part 80c-1 is set to beat a predetermined gradient until the bending of the engaging head 22'at the upstream part 80c-1 is completed, and in the meantime, thedownstream part 80c-2 is heated at a resin softening temperaturelikewise the foregoing embodiments.

In this embodiment having such a structure 9, when theprimary-intermediate surface fastener SF' molded by the die wheel 5arrives at a position between the upper plate 8c and the lower waterbath 80d, the substantially straight substrate sheet 1' and stems 21'are moved in cooling water in the lower water bath 80d via guiderollers, during which a branch of the engaging head 22' is heated at atemperature lower than a resin softening temperature and is graduallybent into a substantially inverted L shape by the upstream part 80c-1ofthe upper plate 80c. As a result, the individual engaging heads 22' arebent with respect to the corresponding stems 21' uniformly at a commonpredetermined bending start point. Specifically, since the substratesheet 1' and the stems 21' are under cooling, they do not becomesoftened due to the heated upper plate 80c so that only the engagingheads 22' above a predetermined level can be bent into a uniform shape.This water cooling method is only an illustrative example, and foraccomplishing the same purpose, the engaging element 2' may have aneasily bendible portion.

The substantially L-bent engaging element 2' is then softened at asoftening temperature and is deformed, as pressed by the downstream part80c-2 of the heated upper plate 80c, to form the protuberances 22a'which is a characterizing part of this invention. The molded surfacefastener SF passed the downstream part 80c-2 is then moved through aslow cooling section, which is at a normal temperature, so that theengaging head 22 would have an increased degree of rigidness as comparedto the remaining portions of the surface fastener SF, as previouslydescribed.

As is apparent from the foregoing description, according to theapparatus of this invention, it is possible to efficiently manufacture amolded surface fastener SF, which is composed of a multiplicity ofunique inverted L-shape engaging elements 2 standing on a substratesheet, each having a pair of protuberances 22a' bulging from oppositeside edges of a substantially flat top surface P, without requiring acomplex process. With such a shape of each engaging element 2, partlysince the engaging head 22 extend substantially straightly from theupper end of the stem, the engaging head 2 has a less itchy touch.Further, since the engaging head 22 can be inclined by an angle morethan 85d° with respect to the stem 21, the engaging head 22 would tendto come into the companion loop 3. Still further, because of theopposite side protuberances of the engaging head 22, it is possible tosecure adequate engaging strength. As a result, reliable engagement canbe retained even with the minute-size companion loops 3, and theprotuberances 2a' serve to hold the loops 3 in sure engagement againstpeeling force which is extend during the engagement. With peeling, theengaging head 22a' bends to flex the stem 21 in the peeling direction sothat the loops 3 are allowed to move smoothly in the removing directionalong the edges of the protuberances 22a' with adequate friction, thusfacilitating removing the loops 3 from the engaging head 22.

According to the unique shape of the engaging element having theprotuberances 22 bulging from the top 22a, it is possible to give thetop surface of the engaging head 22 a less itchy touch and to secureadequate reliable engagement even with minute-size companion loops 3.Further, unlike the conventional mushroom-type engaging element havingan umbrella-shape engaging head projecting in all directions from theupper end of the stem, it is possible to secure a required degree ofpeeling strength and smooth separation. in spite of the minute size ofthe engaging heads, without causing occurrence of a so-called hangingphenomenon in which the neck between the stem and the engaging bead getsentangled with the loops and hence causes damages to either the engagingelements 2 or the loops 3, so that an improved degree of durability canbe achieved.

If the primary surface between SF is molded and solidified by cooling itquickly, but the engaging head heated and pressed to form a pair ofprotuberances is solidified by slow cooling, it is possible to secure anadequate degree of softness for the whole molded surface fastener and toincrease the engaging head in rigidness as compared to the remainingportions of the surface fastener, thus causing an excellent degree ofpeeling resistance and guaranteeing adequate shape stability.

What is claimed is:
 1. A method of manufacturing a molded surfacefastener having a substrate sheet and a multiplicity engaging elementsstanding on one surface of substrate sheet, each of the engagingelements being composed of a stem rising from the one surface of saidsubstrate sheet, and an engaging head projecting from an upper end ofthe stem for detachably engaging a companion loop, said methodcomprising the steps of:(a) molding a primary-intermediate of thesurface fastener with the engaging head of each engaging elementprojecting from the upper end of the stem; (b) positively cooling themolded primary-intermediate surface fastener having the molded engagingelements; (c) continuously moving the cooled and solidifiedprimary-intermediate surface fastener to heating and pressing means; (d)heating and pressing a top of the engaging head from an upper sidethereof by said heating and pressing means to soften the engaging headand, at the same time, to form a pair of protuberances bulging from thetop of the engaging head perpendicularly with respect to a directionlengthwise of the engaging head; and (e) slowly solidifying the moldedsurface fastener having passed said heating and pressing means.
 2. Amethod according to claim 1, wherein a bending angle of the engaginghead with respect to said stem is about 80°˜170°.